1. Field of the Invention
The present invention to a drive apparatus equipped with a ball screw.
2. Description of the Prior Art
An example of this type of drive apparatus of the prior art is disclosed in Utility Model Laid-Open Publication No. 3-47787, a schematic drawing of which is shown in FIG. 1. As shown in the drawing, said drive apparatus is equipped with screw shaft 1, having left and right screw grooves 1a and 1b such that they are mutually intersecting, two nuts 2 and 3 which fit loosely onto said screw shaft 1 and are provided with ball circulating paths (not shown) corresponding to each of said screw grooves 1a and 1b, respectively, and a plurality of balls (not shown) arranged and contained within said ball circulating path which circulate accompanying relative rotation of said screw shaft 1 and nuts 2 and 3.
The above-mentioned nuts 2 and 3 are able to rotate freely as a result of being supporting at both their ends by two ball bearings 6 and 7, respectively. Furthermore, each of said ball bearings 6 and 7 is supported by support member 8 composed of body 8a and covers 8b and 8c. An outer ring collar 9 serves to prevent displacement of the outer rings of ball bearings 6 and 7.
Timing pulleys 10 and 11 are respectively fixed in the centers of the above-mentioned nuts 2 and 3. In addition, two stepping motors 13 and 14 are attached to the upper portion of support member 8 by means of attachment brackets 15 and 16, and timing pulleys 18 and 19 are fit onto the output shafts of each of said stepping motors 13 and 14. Timing belts 21 and 22 are wrapped between mutually corresponding timing pulleys 10 and 18 and mutually corresponding timing pulleys 11 and 19, respectively.
In this drive apparatus, as shown in the drawing, robot hand 23 to be driven is attached to the end of, for example, screw shaft 1. As a result of operating both stepping motors 13 and 14 and suitably changing the directions of rotation and rotating speeds of each nut 2 and 3, backward and forward movement, rotational movement as well as movement combining these can be performed as desired by the robot hand 23 via screw shaft 1. The relationship of movement between nuts 2 and 3 and screw shaft 1 is as shown below.
______________________________________ Difference in No No Different rotating speeds difference difference rotating between both speeds nuts Direction of Same Opposite Same rotation of direction direction direction both nuts State of Rotation Forward and Forward and movement of at that backward backward screw shaft position movement movement only, no while rotation rotating ______________________________________
In this drive apparatus, since forward and backward movement, rotational movement and their compound movements of robot hand 23 to be driven can be performed by only controlling the rotation of two nuts 2 and 3, the structure of the apparatus is simple, and there are many locations at which parts can be shared, thus offering the advantage of reduced costs and so forth.
However, adequate results have yet to be obtained with respect to the problem of reducing the size of the apparatus, which has recently become increasingly important.